package com.wc.alorithm_luogu._二分.P3853_路标设置;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.Arrays;
import java.util.StringTokenizer;

/**
 * @Author congge
 * @Date 2024/3/17 20:05
 * @description https://www.luogu.com.cn/problem/P3853
 */
public class Main {
    static FastReader sc = new FastReader();
    static PrintWriter out = new PrintWriter(System.out);
    static int N = 100010;
    static int[] a = new int[N];
    static int L, n, k;

    public static void main(String[] args) {
        L = sc.nextInt();
        n = sc.nextInt();
        k = sc.nextInt();
        for (int i = 1; i <= n; i++) a[i] = sc.nextInt();
        Arrays.sort(a, 1, n + 1);
        int l = 1, r = L;
        while (l < r) {
            int mid = l + r >> 1;
            if (check(mid)) r = mid;
            else l = mid + 1;
        }
        out.println(l);
        out.flush();
    }

    static boolean check(int mid) {
        int end = 0;
        long res = 0;
        for (int i = 1; i <= n; i++) {
            if (a[i] - end > mid) {
                // 考虑周到, 0 ~ 100, mid = 50, 应该是1根的
                res += (a[i] - end - 1) / mid;
            }
            end = a[i];
        }
        if (L - end > mid) res += (L - end - 1) / mid;
        return res <= k;
    }
}

class FastReader {
    StringTokenizer st;
    BufferedReader br;

    FastReader() {
        br = new BufferedReader(new InputStreamReader(System.in));
    }

    String next() {
        while (st == null || !st.hasMoreElements()) {
            try {
                st = new StringTokenizer(br.readLine());
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        return st.nextToken();
    }

    int nextInt() {
        return Integer.parseInt(next());
    }

    String nextLine() {
        String s = "";
        try {
            s = br.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return s;
    }

    long nextLong() {
        return Long.parseLong(next());
    }

    double nextDouble() {
        return Double.parseDouble(next());
    }

    // 是否由下一个
    boolean hasNext() {
        while (st == null || !st.hasMoreTokens()) {
            try {
                String line = br.readLine();
                if (line == null)
                    return false;
                st = new StringTokenizer(line);
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
        return true;
    }
}
